Pneumatic springs or pneumatic spring struts which are braced between a running gear and a body of a motor vehicle and which have a pneumatic spring bellows, which in turn is fastened between a pneumatic spring cover and a pneumatic spring piston, are known in a multiplicity of embodiments. During operation, the pneumatic spring is subject to an internal positive pressure. The pneumatic spring bellows rolls under load and during spring deflection movements so as to form a roll fold on the outer contour of the concentric pneumatic spring piston which, in the case of a pneumatic spring strut, is fastened to a cylinder tube of the shock-absorbing damper.
In the case of pneumatic springs in the passenger motor vehicle sector, pneumatic spring bellows with the thinnest possible walls are used because these ensure a high level of rolling comfort. In order, in the case of these, to realize a satisfactory load-bearing capacity of the system as a whole, the pneumatic spring bellows or the pneumatic springs are equipped with outer guides, specifically with a tubular sleeve surrounding the pneumatic spring bellows, as a supporting corset or supporting body. It is accordingly possible, for example, for a thin pneumatic spring bellows with a thin light metal sleeve as a supporting body to be optimized for high internal pressures, and thus for high load-bearing capacity, while simultaneously having good harshness characteristics. Here, the outer guides are designed and arranged such that the pneumatic spring bellows can roll, on the one hand, on the outer side of the pneumatic spring rolling piston and, on the other hand, on the inner surface of the outer guide.
This however has the disadvantage that such pneumatic spring bellows, in relation to thick-walled and thus more robust pneumatic spring bellows in the utility vehicle sector, react very much more sensitively to deposits and foreign bodies on the rolling surfaces. The comfortable pneumatic spring bellows, when it rolls over deposits or foreign bodies, very readily reacts with intense abrasion or destruction of its filigree reinforcement members, which can result in failure of the pneumatic spring.
It is therefore necessary that the roll folds of the pneumatic spring bellows be afforded particular protection, which is achieved by way of a protective bellows or corrugated bellows surrounding the pneumatic spring. In particular in the case of externally guided pneumatic springs, use is made of a corrugated bellows to protect the pneumatic spring bellows against fouling (for example dust, sand or stones from the road during driving operation), such as is known for example from DE 103 02 495 A1, incorporated herein by reference. The use of a corrugated bellows however gives rise to the problem that, during spring deflection movements of the pneumatic spring, the air volume of the space surrounded by the corrugated bellows simultaneously changes, and thus an exchange of air must take place between the air enclosed by the corrugated bellows and the contaminated air outside.
In the case of a pneumatic spring strut, the corrugated bellows is attached to the lower end of the shock-absorbing damper piston and to the lower end of the outer guide, such as emerges for example from DE 10 2013 211 644 A1, incorporated herein by reference. The corrugated bellows is fastened to the outer guide in sealed fashion and to the piston with ventilation openings, such that a certain exchange of air can take place at the piston end. It is sought in this way to ensure that no dirt can enter the interior of the corrugated bellows from above, and the dirt that has entered by being sucked in can escape to the outside again in the direction of the running gear.
The arrangement of the corrugated bellows vent at the bottom, facing toward the running gear, of the corrugated bellows has the effect that, during spring compression movements of the pneumatic spring, owing to the associated decrease in volume in the corrugated bellows interior, the air is discharged downward in the direction of the running gear, the pneumatic spring bellows simultaneously exposes an increasing region of the contact surface on the outer guide, and the pneumatic spring rolling piston covers a potentially fouled region. During spring extension movements of the pneumatic spring, owing to the increase in volume in the corrugated bellows interior, potentially contaminated air is sucked in from below, and the pneumatic spring bellows simultaneously covers an increasing and potentially fouled region of the contact surface on the outer guide and exposes contact surface on the piston. A disadvantage is thus that, during spring deflection movements, dust and/or foreign bodies are sucked into the interior of the corrugated bellows. This becomes a problem if such material does not escape to the outside again but passes into the rolling region of the pneumatic spring bellows, which has the effect that the corrugated bellows has lost its required protective function, and damage to the pneumatic spring bellows is not ruled out.
In the case of a pneumatic spring such as is known from DE 10 2009 003 829 A1, incorporated herein by reference, the corrugated bellows is fastened to a collar or projection of the outer guide. The collar is part of the outer guide and has a vent in the form of multiple ventilation bores. Since the pneumatic spring is situated in an upside-down position, the collar of the outer guide faces toward the running gear. The ventilation of the corrugated bellows thus takes place at the bottom of the corrugated bellows. This type of fastening necessitates a certain spacing between outer guide and corrugated bellows, which however has a disadvantageous effect on the usable pneumatic spring bellows volume owing to the small available structural space. An outer guide of said type is also disadvantageous in the manufacturing process, because further manufacturing steps are necessary, for example the deformation of the collar and the formation of the ventilation bores.